Any difference in people's behavior can be explained as being "a difference in brain structure" depending on what you mean by that phrase, because we have different neural pathways that produce different personalities, memories, etc.,

Yes I absolutely agree.

but it is extremely unusual for you to be able to look at a single behavior in an uncontrolled environment and identify a specific characteristic of brain structure that caused it

You're totally right that would be fucking hilarious if I pretended to be a neuroscientist and identified the specific difference in brain structure that caused it and/or larped as a psychologist and formally medically diagnosed the bastard. But I'm not a podcast guru and I'm not saying that.

As I said above, my main point is that I am using the label "psychopath"/"sociopath" as a shorthand for demonstrating really fucked up, comically evil, damaging behaviour (hoarding wealth, snatching candy from a child) to the extent that it's reasonable to assume the person may possibly have an inherent condition partly caused by biological factors.

most people who do things like this do not have that condition

I remember reading somewhere that most billionaires and millionaires display sociopathic tendencies or something. Again, this is not a formal, psychological assessment based on a literature review or deep research.

Among most people, the apparent reason for the majority of difference in behavior can be explained as a matter of socialization/enculturation and other mundane biographical factors

Yes I agree with that for neurotypical people. However, I remember reading somewhere that people who have been formally diagnosed with ASPD have inherent structural differences in their brains. This doesn't imply 'go eugenics' or other dumb shit, it's just that early childhood intervention and support is important.